The first detectable changes in the activities of all dehydrogenases was seen as a slight decrease in the staining intensity of ischemic hemisphere in animals subjected to 2 hours ischemia. The greatest diminution of the demonstrable enzymatic staining product was seen after 9 hours of ischemia. The slight decrease of non-specific acid monophosphatase activity was also not seen prior to 2 hours ischemia. In later stages of ischemia, a loss of enzymatic activity was seen in the severely damaged region, while the surrounding areas showed an increased activity of the acid phosphatase. No significant change in the activity of alkaline phosphatase was demonstrated in ischemic regions at any time. Animals killed within 1 hour of ischemia showed a diminution of phosphorylase activity prominent on the ischemic side. By 6 and 9 hours of ischemia, phosphorylase activity was completely suppressed. Necrotic areas revealed markedly diminished or complete loss of total phosphorylase activity, while the rest of the hemisphere exhibited hyperactivity of the same enzyme and increased glycogen content, especially close to the necrotic areas.